1. Field of the Invention
This invention relates to an ultrasound examination system employing an ultrasound probe to be inserted into an intracavitary portion of human body or the like for ultrasound diagnosis or examination.
2. Description of the Related Art
Ultrasound examination systems are widely used in medical fields, and are usually composed of an ultrasound probe with an ultrasound vibratory element or transducer and an ultrasound image observation terminal which is largely constituted by circuits for transmission and reception of ultrasound signals, circuits for processing ultrasound echo signals and an ultrasound image monitor. Ultrasound energy is transmitted into a body and its echo signals are received by the ultrasound transducer. The received echo signals are transferred to the signal processing circuits of the observation terminal to obtain ultrasonically imaged information, for example, on the condition of intracorporeal tissues and display it on a monitor as an ultrasound image.
In this connection, for ultrasound examination or diagnosis, it is desirable to insert an ultrasound transducer to a position proximal to an intracavitary wall portion of interest and to transmit and receive ultrasound energy at that position for the purpose of enhancing the accuracy and functions of the ultrasound examination or diagnosis, as disclosed in U.S. Pat. No. 4,802,487. For three-dimensional examination, there has been known an ultrasound probe which is adapted to be inserted into a patient's body through a biopsy channel usually provided on an endoscope for insertion of forceps or other biopsy instruments, thereby obtaining ultrasonically imaged information on the tissues of an intracavitary wall portion of interest in addition to endoscopic examination and diagnosis.
For obtaining ultrasound images, it has been the general practice to scan the ultrasound transducer either by an electronic or mechanical scan system. Existing mechanical scan systems include a linear type in which an ultrasound transducer is displaced linearly, and a radial type in which an ultrasound transducer is turned about an axis of rotation. In this regard, from the standpoint of reducing the size of the ultrasound element into a compact form, the mechanical scan system is usually resorted to in case of ultrasound probes of the type which is designed to be inserted into an intracavitary portion of interest through a biopsy channel of an endoscope as mentioned above.
In a system of the mechanical linear scan type, an ultrasound transducer which is mounted at the tip end of an ultrasound probe is inserted into the body in such a way as to contact an intracavitary wall portion or other portion of interest or to face such an intracavitary wall portion through ultrasound transmissive material like water, and the ultrasound probe is pushed forward or backward manually or by the use of a suitable drive means like an electric motor. As the ultrasound transducer is displaced linearly, ultrasound energy is directed into the intracavitary wall portion while receiving return echoes through the ultrasound transducer, and the extent of its displacement is detected by an encoder or other suitable position sensor means to produce position signals according to which an ultrasound image is displayed on a monitor. On the other hand, in an ultrasound examination system of the mechanical radial scan type, the ultrasound probe is connected to a rotational drive means like an electric motor and thereby put in rotation during transmission and reception of ultrasound signals. The scan system of this type is provided with a sensor means to detect the rotational angle of the ultrasound transducer, thereby obtaining position signals for display of ultrasound images.
Of these two types of scanning, either the linear or radial scan is more advantageous depending upon the locality and nature of the ultrasound examination. However, conventional mechanical scan type ultrasound probes are constructed exclusively for either a linear or radial scan mode, without permitting to change the scan mode arbitrarily whenever a necessity arises during examination.